Apparatus and process for isomerizing a hydrocarbon stream

ABSTRACT

One exemplary embodiment can be an apparatus for isomerizing a hydrocarbon stream rich in a C4 hydrocarbon and/or at least one of a C5 and C6 hydrocarbon. The apparatus can include: a vessel containing a fluid including at least one reactant; a fluid transfer device receiving the fluid including at least one reactant from the vessel; at least one drier receiving the fluid including at least one reactant from the fluid transfer device; and a reactor communicating with the at least one drier to receive the fluid including at least one reactant. In addition, the at least one drier may communicate with the vessel at least by sending the fluid including at least one reactant or the regenerant through a fluid tapering device for at least one of regulating the flow and reducing the pressure of the regenerant to the vessel.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Division of copending application Ser. No.12/485,259 filed on Jun. 16, 2009, the contents of which are herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The field of this invention generally relates to an apparatus and aprocess for isomerizing a hydrocarbon stream.

DESCRIPTION OF THE RELATED ART

Isomerization of light paraffins is often conducted to increase theoctane content of gasoline. Generally, such isomerization processes areconducted on separate light hydrocarbon fractions. As an example,isomerization of butane, or pentane and/or hexane (hereinafter may beabbreviated pentane-hexane) is undertaken in separate isomerizationunits to improve the gasoline quality. Typically, both the isomerizationof butane or pentane-hexane are conducted in a fixed-bed liquid/vaporphase or vapor phase process. The reactor can receive a feed of thelight paraffins mixed with a gas including a substantial amount ofhydrogen.

In the isomerization of butane or pentane-hexane, water is a poison thatcan reduce the life expectancy of the reactor catalyst. As such, it isdesirable to remove water before the hydrogen rich gas and/or theparaffin feed reaches the reactor. Consequently, typically both the feedand the gas are passed through separate drier units to remove water.

Often, two driers are utilized in either series or parallel withalternating regeneration operations, whether the fluid being processedis a hydrocarbon containing butane or pentane-hexane or a gas rich inhydrogen. As such, one drier can be in operation while the other driermay be regenerating. At the end of the regeneration, the drier maycontain a liquid regenerant if the drier is a hydrocarbon feed drier, ora gas regenerant if the drier is a gas drier. Depending on thehydrocarbon fraction being isomerized, the regenerant can include mostlyan isomerized product, such as isobutane, or at least one of isopentaneand methylpentane or dimethylbutane (hereinafter may be referred to asisopentane-isohexane) or the regenerant can include a mixture of one ormore different branched, normal, and cyclic compounds. In eitherinstance, generally the regenerant is flushed out of the drier before oras the regenerated drier enters into service. The regenerant is oftenpassed to the reactor.

The regenerant, whether liquid or gas, can cause upsets in thedownstream vessels. Particularly, the gas regenerant can cause a drop inreaction temperatures as the regenerant replaces the hydrogen used inthe reactor, and disrupts the hydrogen:hydrocarbon mole ratio in thereactor. Also, a liquid regenerant can cause a drop in reactortemperatures by replacing a reactant, namely the paraffinic hydrocarbonfeed. In addition, generally the gas regenerant has a heavier molecularweight than the hydrogen rich gas. As a consequence, replacing thehydrogen rich gas may upset the gas flow controls, such as the make-upgas flow, as well as disturbing the pressure controls in a distillationcolumn, that is typically used downstream of the reactor. Thus, there isa desire to lessen the impact after the regeneration of either the gasor feed drier to prevent upsets of downstream vessels.

SUMMARY OF THE INVENTION

One exemplary embodiment can be an apparatus for isomerizing ahydrocarbon stream rich in a C4 hydrocarbon and/or at least one of a C5and C6 hydrocarbon. The apparatus can include: a vessel containing afluid including at least one reactant; a fluid transfer device receivingthe fluid including at least one reactant from the vessel; at least onedrier receiving the fluid including at least one reactant from the fluidtransfer device; and a reactor communicating with the at least one drierto receive the fluid including at least one reactant. In addition, theat least one drier may communicate with the vessel at least by sendingthe fluid including at least one reactant or the regenerant through afluid tapering device. The fluid tapering device may perform at leastone of regulating the flow and reducing the pressure of the regenerantto the vessel. The at least one drier can operate at a first conditionto dry the fluid including at least one reactant and at a secondcondition during regeneration with a regenerant.

Another exemplary embodiment can be a process for regenerating at leastone drier for an apparatus for isomerizing a hydrocarbon stream rich ina C4 hydrocarbon and/or rich in at least one of a C5 and C6 hydrocarbon.The process can include: regenerating the at least one drier with aregenerant wherein the at least one drier contains a used regenerant;and recycling the used regenerant upstream of the at least one drier tomix over a period of time sufficient to dilute the used regenerant witha fluid including at least one reactant to be dried to minimize upsetsin one or more downstream operations.

Yet another exemplary embodiment can be a process for regenerating atleast one drying zone for an apparatus isomerizing a hydrocarbon stream.The process can include: recycling a used regenerant rich in a C4hydrocarbon and/or at least one of a C5 and C6 hydrocarbon upstream ofthe at least one drying zone to mix over a period of time sufficient todilute the used regenerant with a fluid including at least one reactantto be dried for minimizing upsets in one or more downstream operations.

Therefore, the embodiments disclosed herein can minimize upsets inoperations downstream of a fluid drying zone by recycling a usedregenerant upstream of the drying zone. The used regenerant may bepassed through a fluid tapering device to permit dilution of the usedregenerant with an incoming fluid to be dried.

DEFINITIONS

As used herein, the term “stream” can be a stream including varioushydrocarbon molecules, such as straight-chain, branched, or cyclicalkanes, alkenes, alkadienes, and alkynes, and optionally othersubstances, such as gases, e.g., hydrogen, or impurities, such as heavymetals, and sulfur and nitrogen compounds. The stream can also includearomatic and non-aromatic hydrocarbons. Moreover, the hydrocarbonmolecules may be abbreviated C1, C2, C3 . . . Cn where “n” representsthe number of carbon atoms in the hydrocarbon molecule. In addition, theterm “Cn-Cn+1 hydrocarbon,” such as “C5-C6 hydrocarbon,” can mean atleast one of a C5 and C6 hydrocarbon.

As used herein, the term “zone” can refer to an area including one ormore equipment items and/or one or more sub-zones. Equipment items caninclude one or more reactors or reactor vessels, heaters, separators,exchangers, pipes, pumps, compressors, and controllers. Additionally, anequipment item, such as a reactor, drier or vessel, can further includeone or more zones or sub-zones. It should be understood that each zonecan include more equipment and/or vessels than depicted in the drawings.

As used herein, the term “fluid tapering device” generally means adevice that at least directly or indirectly regulates the flow orreduces the pressure of a fluid. Generally, a fluid tapering devicereduces a fluid flow as compared to its absence in e.g., a line, and maythrottle a flow of fluid, as opposed to isolating the fluid. Anexemplary fluid tapering device can include a restriction orifice or acontroller such as a pressure differential indicating controller, apressure indicating controller, a flow indicating controller, a flowindicator or a pressure indicator, typically acting in concert with oneor more other devices, such as a control valve or a restriction orifice.Exemplary fluid tapering devices can include a combination of two ormore components such as a restriction orifice, a flow indicator, apressure differential indicating controller, and a control valve; or aflow indicating controller and a control valve acting in concert. Thefluid tapering device can be installed on one or more lines to alterfluid flow or reduce pressure.

As used herein, the term “fluid transfer device” generally refers to adevice for transporting a fluid. Such devices include pumps typicallyfor liquids, and compressors typically for gases.

As used herein, the term “rich” can mean an amount generally of at leastabout 50%, and preferably about 70%, by mole, of a compound or class ofcompounds in a stream.

As used herein, the term “substantially” can mean an amount generally ofat least about 90%, preferably about 95%, and optimally about 99%, bymole, of a compound or class of compounds in a stream.

As used herein, the term “absorption” can refer to the retention of amaterial in a bed containing an absorbent and/or adsorbent by anychemical or physical interaction between a material, such as water, andthe bed, and includes, but is not limited to, adsorption, and/orabsorption. The removal of the material from an absorbent may bereferred to herein as “desorption.”

As used herein, the term “used regenerant” can refer to a regenerantthat has been used for drying or desorbing, or that has been circulatedthrough one or more vessels or equipment items, such as a drier. A usedregenerant may or may not have desorbed a material, such as water, butmay be present in a vessel after the vessel contents, such as amolecular sieve, have been regenerated.

As used herein, the term “coupled” can mean two items, directly orindirectly, joined, fastened, associated, connected, or formedintegrally together either by chemical or mechanical means, by processesincluding stamping, molding, or welding. What is more, two items can becoupled by the use of a third component such as a mechanical fastener,e.g. a screw, a nail, a staple, or a rivet; an adhesive; or a solder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of an exemplary apparatus forisomerizing a fluid.

FIG. 2A is a schematic depiction of an exemplary first fluid dryingunit.

FIG. 2B is a schematic depiction of an exemplary second fluid dryingunit.

FIG. 3 is a schematic depiction of an exemplary third fluid drying unit.

DETAILED DESCRIPTION

An apparatus 100 for isomerizing a hydrocarbon stream is depicted inFIG. 1. Generally, the apparatus 100 can receive a fluid including atleast one reactant 110 in either a line 210 or a line 410. Usually, thefluid 110 can be a liquid hydrocarbon stream in the line 210 or a gasrich in hydrogen in the line 410. The liquid hydrocarbon stream can berich in a C4 hydrocarbon, such as butane, if the apparatus 100 is a C4isomerization apparatus. Alternatively, the liquid hydrocarbon streamcan be rich in a C5-C6 hydrocarbon, such as pentane-hexane, if theapparatus 100 is a C5-C6 isomerization apparatus. Exemplary apparatusesof both types are disclosed in, e.g., Nelson A. Cusher, UOP ButamerProcess and UOP Penex Process of the Handbook of Petroleum RefiningProcesses, Third Edition, Robert A. Meyers, Editor, 2004, pp. 9.7-9.27.However, the apparatus 100 may also be utilized for simultaneouslyisomerizing a stream of one or more butanes, one or more pentanes, andone or more hexanes in some exemplary embodiments. Note that theisomerization reactions include those having largely normal paraffins asfeedstock and branched paraffins as isomerate product as well as thosehaving largely branched paraffins as feedstock and normal paraffins asisomerate product. In other words, the liquid hydrocarbon stream can berich in isobutane or branched C5-C6 hydrocarbon. Other isomerizationreactions involving the C4 or C5-C6 hydrocarbons are within the scope ofthe invention as well.

To simplify the discussion below, terms such as “liquid hydrocarbon” and“regenerant” may be referred to generically and should be understood tobe applicable to, e.g., either a C4 isomerization apparatus or a C5-C6isomerization apparatus. As an example, a hydrocarbon stream rich in aC4 hydrocarbon can be isomerized in a C4 isomerization reactor and anisomerized C4 hydrocarbon product can be used as a regenerant in a C4isomerization apparatus. Likewise, a hydrocarbon stream rich in a C5-C6hydrocarbon can be isomerized in a C5-C6 isomerization reactor, and anisomerized C5-C6 hydrocarbon product can be used as a regenerant in aC5-C6 isomerization apparatus.

The apparatus 100 can include one or more vessels 130, one or more fluidtransfer devices 140, one or more drying zones 150, and one or moredownstream vessels 160. The one or more vessels 130 can include a surgedrum 230 or a distillation column receiver 230 (may be hereinafterreferred to collectively as a surge drum 230) for receiving ahydrocarbon stream and a suction drum 430 for receiving a gas rich inhydrogen, such as a recycled hydrogen gas stream.

The one or more fluid transfer devices 140 can include a pump 240 forreceiving the hydrocarbon stream from the surge drum 230, and acompressor 440 for receiving the gas rich in hydrogen from the suctiondrum 430. The one or more drying zones 150 can include a liquid dryingzone 250 for receiving the liquid hydrocarbon stream from the pump 240,and a gas drying zone 450 for receiving the gas rich in hydrogen fromthe compressor 440.

Generally, the surge drum 230, the pump 240, and the liquid drying zone250 are comprised in a first fluid drying unit 200. Generally, theliquid hydrocarbon stream is provided by the line 210 and exits via aline 310. Also, the suction drum 430, the compressor 440, and the gasdrying zone 450 are comprised in a second fluid drying unit 400.Generally, a gas is provided in the line 410 and exits via a line 510.Both units 200 and 400 are discussed in further detail below.

The one or more downstream vessels 160 can be segregated into a reactionzone 170 and a fractionation zone 180 where one or more downstreamoperations can occur. After exiting the drying zones 250 and 450, thehydrocarbon stream and the gas rich in hydrogen may be combined in thereaction zone 170. The reaction zone 170 can include a first reactor 172and a second reactor 174 in series with the first reactor 172. Althoughonly the first reactor 172 and second reactor 174 are depicted, itshould be understood that the reaction zone 170 can further includeother vessels and/or equipment, such as one or more heaters, a recyclegas compressor, a separator vessel, and additional reactors.Alternatively, the reactors 172 and 174 can be placed in singleoperation. The effluent from the reaction zone 170 can exit a line 176to the fractionation zone 180.

The fractionation zone 180 can include a distillation column 192producing one or more separated products 182. Although one distillationcolumn 192 is depicted, two or more distillation columns may be operatedin series and/or in parallel. The one or more separated products 182 mayinclude a first product of one or more gases routed to e.g., fuel gas,in a line 184 and a second product or isomerized product in a line 186.A portion of the second product can be withdrawn through a line 188 andused as a regenerant. Used regenerant can be returned to the isomerizedproduct in a line 190, as hereinafter described. The combined stream canbe sent to an isomerized product storage tank, a distillation column, oranother process unit.

Referring to FIG. 2, the first fluid drying unit 200 is depicted. Thefirst fluid drying unit 200 can be used to dry a liquid hydrocarbonstream, typically a light normal paraffin stream. Usually, the firstfluid drying unit 200 includes the surge drum 230, the pump 240, atleast one drier 254, one or more valves 260, a fluid tapering device290, and a heater 300.

Preferably, the at least one drier 254 includes a first liquid drier 256and a second liquid drier 258. The drier 256 and the drier 258 can becomprised in the liquid drying zone 250 as depicted in FIG. 1. Moreover,each drier 256 and 258 can contain a molecular sieve where absorption ofwater occurs and a respective internal drying zone or sub-zone.Generally, each drier 256 and 258 operates at a first condition to drythe hydrocarbon stream passing through the drier and a second conditionto regenerate the drier. Typically, the driers 256 and 258 are in seriesand regenerate alternatively with the other drier drying.

The one or more valves 260 can include a valve 262, a valve 264, a valve264′, a valve 266, a valve 268, a valve 270, a valve 270′, a valve 272,a valve 274, a valve 276, a valve 278, a valve 280, a valve 282, and avalve 284. Various combinations of valves 260 can be opened and closedto direct process streams for conducting the first and secondconditions.

In this exemplary embodiment, the fluid tapering device 290 can includea flow indicating controller 292 communicating with a control valve 294,and can regulate the flow and reduce the pressure of the regenerant. Theheater 300 can include a steam heater 304 and a superheater 308 forheating the regenerant to operate at the second condition forregenerating a drier. Particularly, the steam heater 304 can be used tovaporize the regenerant before the superheater 308 brings the regenerantto a sufficient temperature to desorb water from the molecular sieve ofthe drier 256 or 258.

In one exemplary regeneration operation, the liquid hydrocarbon streamcan be passed through the line 210 into the surge drum 230. Afterwards,the liquid hydrocarbon stream may pass to the pump 240 and then to thefirst drier 256 or the second drier 258. Generally, the liquidhydrocarbon stream enters one of the driers, as an example, the drier258, and passes through the valves 278 and 280 and into the drier 258 tohave water removed. Afterwards, the dry liquid hydrocarbon stream canpass through the valves 272 and 268 and into the line 310 to thereaction zone 170 as depicted in FIG. 1. Typically, the liquidhydrocarbon stream is being dried in the drier 258 with the valves 266,270, 270′ and 276 closed, while the valves 278, 280, 268 and 272 areopen.

Meanwhile, the other drier 256 can be regenerated. Generally, theregeneration is a multiple stage process using a liquid regenerant fromthe line 188 of FIG. 1, which may be passed to the heater 300. Duringthe regeneration, the regenerant may be heated in stages with the steamheater 304 and then with both the steam heater 304 and the superheater308 until the regenerant can be of sufficient temperature to desorb thewater from the molecular sieve. Generally, the regenerant passes throughthe steam heater 304 and the superheater 308 through a line 288 and thevalve 282 to the top of the drier 256. Subsequently, the regenerant canpass through the drier 256, and through the valve 284 and a line 298before being cooled with e.g., a cooling water exchanger. Next, theregenerant can be routed via the line 190 to isomerized product asdepicted in FIG. 1.

Afterwards, the regenerant is slowly cooled by first turning off thesuperheater 308 and then the steam heater 304 while continually passingthe regenerant through the drier 256. Thus, the drier 256 and associatedequipment can be cooled in stages to slowly ramp down the temperatures.At the end of the regeneration process, the drier 256 generally containsthe liquid regenerant.

By using the liquid hydrocarbon stream, the used regenerant can beforced upflow from the drier 256 through the opened valves 262 and 264to a line 286 as depicted in FIG. 2A. Alternatively, by using the liquidhydrocarbon stream, the used regenerant can be forced downflow from thedrier 256 through the opened valves 274 and 264′ to a line 286 asdepicted in FIG. 2B. The liquid used regenerant may pass through a flowindicating controller 292 communicating with a control valve 294.Generally, the control valve 294 regulates the flow of the liquid backto or upstream of the surge drum 230. As the used regenerant passesthrough the control valve 294, the pressure of the fluid may drop topermit its passage into the surge drum 230. Typically, there is a largepressure difference of the used regenerant upstream of the control valve294 and the surge drum 230. Using the control valve 294 to reduce thepressure of the used regenerant can prevent a “blow-out” of the surgedrum 230. Usually, it is desired to not only regulate the flow of theused regenerant, but also to reduce its pressure. Regulating the returnof the used regenerant to the surge drum 230 can mix and dilute the usedregenerant with the incoming fluid in the line 210 to reduce the impacton downstream equipment, operations and/or vessels, such as thosevessels 160 comprised in the reaction zone 170 and the fractionationzone 180 as depicted in FIG. 1. Although a flow indicating controllerand a control valve have been disclosed, it should be understood thatother types of fluid tapering devices may be used, such as a restrictionorifice or other type of device. Furthermore, during the passage of theused regenerant back to the surge drum 230, a period of time can becalculated for the desired dilution of the regenerant. The flowcontroller 292 can be adjusted to increase or decrease the flow of theregenerant through the control valve 294. Generally, the presence of thefluid tapering device 290, such as the control valve 294, can reduce theamount of liquid flowing back to the surge drum 230 than otherwise wouldoccur in its absence.

As discussed above, the drier 258 may be operated at the first conditionand the other drier 256 can be operated at the second condition. Itshould be understood that FIG. 2A and FIG. 2B are merely schematics andadditional lines and/or valves can be provided to operate the drier 256at the first condition, the drier 258 at the second condition, and bothdriers in series. As an example, the driers 256 and 258 can be placedback in series operation with, e.g., the drier 256 in a lag positionwith respect to the drier 258, after regeneration.

Referring to FIG. 3, the second fluid drying unit 400 is depicted. Thesecond fluid drying unit 400 can be used to dry a gas stream, such as agas rich in hydrogen. Usually, the second fluid drying unit 400 includesthe suction drum 430, the compressor 440, at least one drier 454, one ormore valves 460, a fluid tapering device 490, and a heater 500. Thesecond fluid drying unit 400 may also include another fluid taperingdevice 590, which may be used in the alternative as describedhereinafter.

Preferably, at least one drier 454 includes a first gas drier 456 and asecond gas drier 458. The drier 456 and the drier 458 can be comprisedin the gas drying zone 450 depicted in FIG. 1. Moreover, each drier 456and 458 can contain a molecular sieve where absorption of water occursand include a respective internal drying zone or sub-zone. Generally,each drier 456 and 458 operates at a first condition to dry the gas richin hydrogen passing through the drier 456 or 458 and a second conditionto regenerate the drier 456 or 458. Typically, the driers 456 and 458are in series and regenerate alternatively with the other drier drying.

The one or more valves 460 can include a valve 462, a valve 464, a valve466, a valve 468, a valve 470, a valve 472, a valve 474, a valve 476, avalve 478, a valve 480, valve 482, a valve 484, a valve 550, a valve554, and a valve 562. Various combinations of valves 460 can be openedand closed to direct process streams for conducting the first and secondconditions.

In this exemplary embodiment, the fluid tapering device 490 can includea restriction orifice 492 and a flow indicator 494, and can reduce theflow and reduce the pressure of the regenerant. The heater 500 caninclude a steam heater 504 and a superheater 508 for heating theregenerant to operate in the second condition for regenerating a drier.Particularly, the steam heater 504 can be used to vaporize theregenerant before the superheater 508 brings the regenerant to asufficient temperature to remove water from the molecular sieve of thedrier 456 or 458.

In one exemplary regeneration operation, the gas, such as a gas rich inhydrogen, can enter through the line 410 to the suction drum 430. Thegas can then pass to the compressor 440, and then to one of the driers456 and 458. As an example, the gas can enter through the valves 478 and480 into the drier 458 to desorb water. Afterwards, the dry gas can passthrough valves 472 and 468 into a line 510 to be combined with theliquid hydrocarbon stream before entering the reaction zone 170 asdepicted in FIG. 1. Typically, the gas stream is dried in the drier 458with the valves 466, 470, 474 and 476 are closed, while the valves 478,480, 468, and 472 are open.

Meanwhile, the other drier 456 can be regenerated. Generally, theregeneration is a multiple stage process using a liquid regenerant fromthe line 188 of FIG. 1, which may be passed to the heater 500. Duringthe regeneration, the regenerant may be heated in stages with the steamheater 504 and then with both the steam heater 504 and the superheater508 until the regenerant is of sufficient temperature to desorb waterfrom the molecular sieve. Generally, the regenerant passes through thesteam heater 504 and the superheater 508 through a line 488 and thevalve 482 to the top of the drier 456. Subsequently, the regenerant maypass through the drier 456, through the valve 484, and a line 498 beforebeing cooled with, e.g., a cooling water exchanger, and routed to theisomerized product in the line 190 as depicted in FIG. 1. Typically, thevalves 462, 474, 476, and 562 are closed.

Afterwards, the regenerant can be slowly cooled by first turning off thesuperheater 508 while continually passing the regenerant through thedrier 456. Thus, the drier 456 and associated equipment can be cooled toslowly ramp down the temperatures. At the end of the regenerationprocess, the drier 456 generally contains the regenerant as a gas.

By using the gas rich in hydrogen, the used regenerant can be forcedfrom the drier 456 through the opened valves 462, 464, and 550 with thevalve 554 closed to a line 486. The gaseous used regenerant may passthrough a flow indicator 494 and a restriction orifice 492. Generally,the restriction orifice 492 reduces the flow and also reduces thepressure of the regenerant recycled back to or upstream of the suctiondrum 430. Due to the pressure differential of the used regenerant acrossthe restriction orifice 492, reducing the pressure to a desired levelcan prevent a “blow-out” of the suction drum 430. Also, it is typicallydesired to reduce the flow of the used regenerant to permit its dilutionin the suction drum 430. Mixing the used regenerant with the incomingfluid in the line 410 can dilute the regenerant and reduce the impact ondownstream operations, downstream equipment, and/or downstream vessels160, such as those vessels comprised in the reaction zone 170 and thefractionation zone 180 as depicted in FIG. 1. Although a flow indicator494 and a restriction orifice 492 have been disclosed, it should beunderstood that other types of fluid tapering devices may be used, suchas a flow indicating controller communicating with a flow control valveor one or more other type devices. Generally, the presence of the fluidtapering device 490, such as the restriction orifice 492, can reduce theamount of gas sent back to the suction drum 430 than otherwise wouldoccur in its absence.

By selecting the restriction orifice size, the length of recycle can bedesigned to sufficiently dilute the used regenerant in the suction drum430 before being passed through at least one of the driers 454 and thento the reaction zone 170 as depicted in FIG. 1. By reducing the flow andpressure of the used regenerant back to the suction drum 430, the usedregenerant can be diluted with other gases entering the suction drum 430through the line 410. Thus the impact on the one or more downstreamoperations, downstream equipment and/or downstream vessels 160, asdepicted in FIG. 1, may be minimized.

An alternative embodiment can prevent the condensation and absorption ofthe regenerant on the molecular sieve to expedite removal of the usedregenerant from the regenerated drier by lowering the pressure of thegas rich in hydrogen entering the drier 456. In this exemplaryembodiment, the drier 456 generally contains the used regenerant as agas at the end of the regeneration process. Using the gas rich inhydrogen, the gas rich in hydrogen can pass through the open valve 476with the valve 474 closed. The gas rich in hydrogen can pass into a line564, and through the fluid tapering device 590 including a flowindicator 594 and a restriction orifice 592 to reduce the pressure ofthe gas. Afterwards, the gas can pass through the open valve 562 andinto the drier 456. The regenerant can be forced from the drier 456through the opened valves 462 and 464. Next, the valve 554 can be openedand the valve 550 can be closed so the regenerant may bypass the fluidtapering device 490 via a line 558 and enter the line 486. Subsequently,the regenerant may pass upstream or to the suction drum or receiver 430,as described above. Thus, the fluid tapering device 590 may indirectlyregulate the flow and reduce the pressure of the used regenerant, andkeep the pressure inside the drier 456 below the saturation pressure ofthe used regenerant.

As discussed above, the drier 458 may be operated at the first conditionand the other drier 456 may be operated at the second condition. Itshould be understood that additional lines and/or valves can be providedto operate the drier 456 at the first condition, the drier 458 at thesecond condition, and both driers in series. As an example, the driers456 and 458 can be placed back in series operation with, e.g., the drier456 in a lag position with respect to the drier 458, after regeneration.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The preceding preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing, all temperatures are set forth uncorrected in degreesCelsius and, all parts and percentages are by mole, unless otherwiseindicated.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A process for regenerating at least one drier for an apparatus for isomerizing a hydrocarbon stream rich in at least one hydrocarbon selected from the group consisting of at least one C4 hydrocarbon, at least one C5 hydrocarbon, at least one C6 hydrocarbon, and mixtures thereof, comprising: A) regenerating the at least one drier with a regenerant wherein the at least one drier contains a used regenerant; and B) recycling the used regenerant upstream of the at least one drier to mix over a period of time sufficient to dilute the used regenerant with a fluid comprising a gas rich in hydrogen to be dried to minimize upsets in one or more downstream operations.
 2. The process according to claim 1, wherein the fluid comprises a liquid rich in at least one hydrocarbon selected from the group consisting of at least one C4 hydrocarbon, at least one C5 hydrocarbon, at least one C6 hydrocarbon, and mixtures thereof.
 3. The process according to claim 1, wherein the period of time is calculated to dilute the used regenerant with the fluid comprising at least one reactant to minimize upsets in at least one of a downstream reaction zone and a fractionation zone.
 4. The process according to claim 1, wherein the at least one drier is a liquid feed drier and the used regenerant is recycled upflow through the at least one liquid feed drier.
 5. The process according to claim 4, wherein the at least one drier is a liquid feed drier and the used regenerant is recycled downflow through the at least one liquid feed drier.
 6. The process according to claim 5, wherein the at least one drier is a gas drier. 